1. Field of the Invention
The present invention generally relates to a wavelength monitoring device for monitoring the wavelength of a laser light, its adjusting method, a wavelength stabilizing light source for emitting a laser light of a stable wavelength and also a transmission system provided with a plurality of such wavelength stabilizing light sources, and more particularly to an industrial technique which is applicable to the method of wavelength division multiplexing transmission (hereinafter referred to just as xe2x80x9cWDMxe2x80x9d).
2. Description of the Related Art
In the recent trend of optical communications, various transmission methods have been investigated to cope with a vastly increasing amount of information to be transmitted. Among those transmission methods, the above-mentioned WDM method has been developed for increasing transmission capacity by multiplexing various optical signals of different wavelengths and transmitting the thus multiplexed optical signals concurrently. However, even though a plurality of optical signals of different wavelengths are multiplexed and transmitted concurrently, no wavelength outside the band in which it is amplifiable by an amplifier can be used, and thus, in order to multiplex various optical signals and transmit concurrently the thus multiplexed light signals, it will be the most significant requirement to reduce the wavelength of individual optical signals, and also reduce the intervals between the wavelength of individual optical signals. In order to meet this requirement, a technique for monitoring the wavelength of optical signals of a narrow band and stabilizing the thus monitored wavelength in high precision has been required.
(First Prior Art)
FIG. 1 is a schematic diagram showing the wavelength monitoring device according to a first prior art as described in xe2x80x9cConvention of Communication Society of 1998xe2x80x9d, the transaction of the Institute of Electronics, Communication, and Information Engineers (B-10-180). In the figure, reference numeral 101 denotes a first beam splitter for separating an incident light, numeral 102 denotes a second beam splitter for separating the input light passed through the first beam splitter 101, 103 denotes a first photo-diode (hereinafter referred to just as xe2x80x9cPDxe2x80x9d) for receiving one part of the incident light separated by the first beam splitter 101, 104 denotes a second PD for receiving one part of the input light separated by the second beam splitter 102, 105 denotes a first Fabry-Perrot Etalon filter (hereinafter referred to just as xe2x80x9cFP Etalon Filterxe2x80x9d) disposed between the first beam splitter 101 and the first PD 103, 106 denotes a second FP Etalon filter disposed between the second beam splitter 102 and the second PD 104. Here, the first FP Etalon filter 105 and the second FP Etalon filter 106 have different wavelength transmission characteristics.
The operation of the device is explained below.
One part of the incident light separated in the first beam splitter 101 is transmitted through the first FP Etalon filter 105, and is received by the first PD 103 thereafter. Similarly, one part of the input light separated in the second beam splitter 102 is transmitted through the second FP Etalon Filter 106, and is received by the second PD 104 thereafter.
Since the first Etalon filter 105 and the second Etalon filter 106 have different wavelength transmission characteristics from each other, the signals emit from these first and second PDS 103 and 104 show respectively different wave characteristics from each other. For this reason, as to the difference between the output signal from the first PD 103 and that from the second PD 104, the strength of the difference signal therebetween becomes zero if the input light is of the wavelength at which the signal strength of the light transmitted through the first Etalon filter 105 and that transmitted through the second Etalon filter 106 are made equal to each other. Due to this, if the wavelength at which the strength of the difference signal becomes zero is made a reference wavelength, the degree of a change in the wavelength of the incident light varied from the reference wavelength can be represented by the strength of the difference signal having either a positive or a negative symbol.
(Second Prior Art)
FIG. 2 is a schematic diagram showing the wavelength monitoring device according to the second prior art, which is disclosed in the U.S. Pat. No. 5,825,792. In the figure, reference numeral 111 denotes a DFB (Distributed Feed Back) semiconductor laser, numeral 112 denotes an optical lens for adjusting the width of the beam spot emitted from the DFB semiconductor laser 111, numerals 113 and 114 denote respectively a first and a second PDs for receiving lights emitted from the semiconductor laser 111 and transmitted through the optical lens 112, numeral 115 denotes an FP Etalon filter disposed between the optical lens 112 and both the first and second PDs 113 and 114, numeral 116 denotes a subtractor for obtaining the difference between the signal output from the first PD 113 and that output from the second PD 114, and feeds the thus obtained value back to the DFB semiconductor laser 111. The first and the second PDs are disposed separately from each other within the light transmitted through the FP Etalon filter 115, and are fixed to a common base 117. The FP Etalon filter 115 is disposed in an inclined manner with respect to the optical axis.
The operation of the device is explained below.
The width of the beam spot of the light emitted from the DFB semiconductor laser 111 is adjusted at the optical lens 112, transmitted through the FP Etalon filter 115, and finally received by the first and second PDs 113 and 114.
Since the FP Etalon filter 115 is disposed in an inclined manner with respect to the optical axis, an incident angle against the FP Etalon filter 115 varies depending on the position of the incident light beam, and the wavelength transmission characteristic also varies in accordance with the thus varied incident angle. For this reason, the signals output from the first PD 113 and the second PD 114 disposed separately from each other within the light beam transmitted through the FP Etalon filter 115 have respectively different wavelength characteristics. In other words, FP Etalon filters having different wavelength transmission characteristics from each other are not required, but only one FP Etalon filter is required for obtaining two signals having different wavelength transmission characteristics from each other. Due to this, when the first and the PD filters 113 and 114 are disposed in such a manner that the strength of the incident lights thereto are made equal at the reference wavelength xcex0, the strength of the difference signal from the subtractor 116 becomes 0 at the reference wavelength xcex0, so that the change in the wavelength of the emitted light from the DFB semiconductor laser 111 varied from the reference wavelenth can be represented by the strength of the difference signal having either a positive or a negative symbol.
The difference signal is fed back to the DFB semiconductor laser 111, and the wavelength of the light emitted from the DFB semiconductor laser 111 is thus stabilized.
Since the wavelength monitoring device according to the first prior art is configured as mentioned before, wherein two beam splitters, two PDs, and two FP Etalon filters are provided, there has been a problem that the number of components is increased, and thus the total size of the device is thereby increased.
In addition to this, since two beam splitters are used, three light propagating directions are generated, and thus the alignment thereof is quite difficult.
Still further, since the wavelength transmission characteristics of these two FP Etalon filters used therein vary due to a temperature change, there has been such a problem that the wavelength at which the strength of the difference signal becomes zero is deviated due to the temperature change, and thus correction in accordance with temperature change is required. Specially, in the case of the first prior art in which two FP Etalon filters whose wavelength transmission characteristics vary due to a temperature change are used, there has been a drawback that the wavelength transmission characteristic varies per each FP Etalon filter due to a temperature change, so that correction in compliance with the temperature change is made difficult, and subsequently a precise wavelength monitoring cannot be expected.
Still further, the wavelength monitoring device according to the second prior art is configured as explained above, wherein although two signals having different wavelength characteristics from each other are obtained by disposing the FP Etalon filter in an inclined manner with respect to the optical axis, even within the angle in which the light receiving surface of each PD can expect the DFB semiconductor laser, the incident angle at which the light enters is different depending on the position of the light beam, so that the output signal from each PD is represented just as an average value within the laser light expecting angle, and thus a precise wavelength monitoring is not made possible. In fact, the precision becomes worse, when the open surface area of the FP Etalon filter is expanded and the light receiving surface is made wider.
Still further, the light emitted from the DFP semiconductor laser is not collimated and is propagated with a certain spread. Further since the wavelength characteristic of the output signal from each PD depends on the incident angle of the light with respect to the FP Etalon filter, the position of the first and the second PDs, and that of the FP Etalon filter with respect to the optical axis are extremely limited, and thus the alignment thereof is made difficult.
Yet still further, since the wavelength transmission characteristic of these two FP Etalon filters used therein vary due to a temperature change, the wavelength at which the difference signal becomes zero due to the temperature change, and thus there has been a problem that correction in compliance with the temperature change must be carried out.
The present invention has been proposed to solve the problems aforementioned, and it is an object of the present invention to provide a wavelength monitoring device of a small size that enables an easy alignment and also an accurate wavelength monitoring, together with the adjusting method thereof, and also to provide a wavelength stabilizing light source and a transmission system provided with a plurality of those light sources, by use of a wavelength-monitored signal output from the wavelength monitoring device.
It is also another object of the present invention to provide a wavelength monitoring device that obviates any correction in compliance with a temperature change, together with the adjusting method thereof, and also to provide a wavelength stabilizing light source and a transmission system provided with a plurality of those light sources, by use of a wavelength-monitored signal output from the wavelength monitoring device.
The wavelength monitoring device according to the present invention comprises a polarization state changing means having a first birefringent crystal, which inputs a polarized laser light and changes the polarization state of the input laser light after it is transmitted through the first birefringent crystal, in accordance with the wavelength of the input laser light, a polarized light selecting and receiving means, which inputs the laser light transmitted through the polarization state changing means and selectively receives a predetermined linearly polarized component, and a wavelength detection method that monitors the wavelength of the laser light input to the first birefringent crystal by use of ran optical signal output from the polarized light selecting and receiving means.
By this configuration, a wavelength monitoring device of a small size, easy alignment, and of high precision can be obtained.
A wavelength monitoring device according to the present invention is constructed such that the polarization state changing means further comprises a second birefringent crystal, which inputs the laser light transmitted through the first birefringent crystal and changes the polarization state of the laser light after it is transmitted through the second birefringent crystal, in accordance with the wavelength of the input laser light, wherein the first and the second birefringent crystals are disposed according to the value of a change in the difference between the refraction index of the first birefringent crystal and that of the second birefringent crystal due to a temperature change, and the length of the propagating direction of the first birefringent crystal and that of the second birefringent crystal are set to a predetermined length, so as to offset the discrepancy between the phase shifted value in the fast axis direction and that in the slow axis direction caused by the change in the difference between the refractive index in the fast axis direction and that in the slow axis direction and also by the change in the length of the propagating direction of the laser light of the first birefringent crystal, which changes being caused due to a temperature change.
By this configuration, a wavelength monitoring device that requires no correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the laser light input to the first birefringent crystal is a linearly polarized light.
By this configuration, a wavelength monitoring device in which the positioning of the birefringent crystal is quite easy can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is disposed in such a manner that its fast axis is inclined for 45 degrees with respect to the polarizing direction of the laser light input to the first birefringent crystal.
The wavelength monitoring device according to the present invention is constructed such that the polarized light selecting and receiving mean comprises a polarized light separating means for inputting the laser light transmitted through the polarization state changing means and extracting a predetermined linearly polarized component therefrom, and a polarized light receiving means for receiving the linearly polarized component extracted from the polarized light separating means.
The wavelength monitoring device according to the present invention further comprising: a laser light receiving means for receiving the laser light that has not passed through the polarized light separating means, and a strength detection means for monitoring the change in the strength of a laser light source whose wavelength is to be monitored, by use of an optical signal output from the laser light receiving means.
By this configuration, a wavelength monitoring device capable of monitoring the strength of a laser light can be obtained.
The wavelength monitoring device according to the present invention further comprising a light condensing means for condensing the linearly polarized component extracted from the polarized light separating means between the polarized light separating means and the polarized light receiving means.
By this configuration, a small-sized wavelength monitoring device having the polarized light receiving means of a small size can be obtained.
The wavelength monitoring device according to the present invention is the one in which the polarized light separating means is provided on an input-side surface of the polarized light receiving means.
By this construction, a wavelength monitoring device having a small number of components used therein and its alignment is thus facilitated can be obtained.
The wavelength monitoring device according to the present invention is the one in which the polarized light separating means inputs a laser light transmitted through the polarization state changing means and separates it into a first linearly polarized component and a second linearly polarized component polarizing at right angles to each other and extracts the thus separated components, and the polarized light receiving means further comprises a light receiving means for the first component for receiving the first linearly polarized component extracted from the polarized light separating means, and also a light receiving means for the second component for receiving the second linearly polarized component extracted from the polarized light separating means.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high precision by use of two signals of different wavelength characteristics can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the polarized light separating means further comprises a polarizer for transmitting either one of the first linearly polarized component and the second linearly polarized component, while reflecting the other.
By this configuration, a wavelength monitoring device capable of easily separating the laser light transmitted through the polarization state changing means into the p-polarized component and the s-polarized component can be obtained
The wavelength monitoring device according to the present invention is constructed such that the polarized light separating means further comprises a 2-quadrant polarizer provided with a first area for inputting a laser light transmitted through the polarization state changing means and transmitting only the first linearly polarized component, and a second area for inputting a laser light transmitted through the polarization state changing means and transmitting only the second linearly polarized component.
By this configuration, the laser light propagating direction is made only to one direction, so that a wavelength monitoring device capable of performing an easy alignment can be obtained.
The wavelength monitoring device according to the present invention is the one in which the polarized light separating means further comprises a laser light 3-dividing element provided with a first area for inputting a laser light transmitted through the polarization state changing means and transmitting only the first linearly polarized component, a second area for inputting a laser light transmitted through the polarization state changing means and transmitting only the second linearly polarized component, and a third area for inputting a laser light transmitted through the polarization state changing means and transmitting it without changing its polarization state.
By this configuration, the laser light propagating direction is made only to one direction, so that a wavelength monitoring device capable of performing an easy alignment can be obtained.
The wavelength monitoring device according to the present invention further comprising a laser light receiving means for receiving a laser light transmitted through the third area, and a strength detection circuit for monitoring the change in a laser light source whose wavelength is to be monitored, by use of an optical signal output from the laser light receiving means.
By this configuration, a wavelength monitoring device capable of monitoring the strength of the laser light can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the 2-quadrant polarizer is provided on an output-side surface of the polarization state changing means.
By this configuration, a wavelength monitoring device having a small number of components used therein and its alignment is thus facilitated can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the laser light 3-dividing element is provided on an output-side surface of the polarization state changing means.
By this configuration, a wavelength monitoring device having a small number of components used therein and its alignment is thus facilitated can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the light receiving element for the first component further comprises a first and a second light receiving elements, and the light receiving element for the second component further comprises a third and a fourth light receiving elements.
By this configuration, a wavelength monitoring device capable of easily obtaining a difference signal and a sum signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the first to fourth light receiving elements are provided on a same base plate.
By this configuration, a wavelength monitoring device having a small number of components used therein and its alignment is thus facilitated can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal, the polarized light separating means and the polarized light selecting and receiving means are disposed such that the input-side and output-side surfaces of each are inclined with respect to the laser light propagating direction.
By this configuration, a wavelength monitoring device having no returned light reflected on the side surfaces can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises a divider for outputting the ratio of the optical signal output from the polarized light receiving means to the strength-monitored signal output from the strength detection means.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a quotient signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises a subtractor for outputting the difference between the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a difference signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises an adder for outputting the sum of the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a sum signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises: a subtractor for outputting the difference between the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component, an adder for outputting the sum of the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component, and a divider for outputting the ratio of the difference signal output from the subtractor to the sun signal output from the adder.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a quotient signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises: an adder for outputting the sum of the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component, and a divider for outputting the ratio of the optical signal output from either one of the light receiving means for the first component and the optical signal output from the light receiving means for the second component to the sum signal output from the adder.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a quotient signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises: a subtractor for outputting the difference between the optical signal output from the light receiving means for the first component and the optical signal output from the light receiving means for the second component, and a divider for outputting the ratio of the difference signal output from the subtractor to the strength-monitored signal output from the strength detection means.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring in high accuracy by use of a quotient signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the wavelength detection means further comprises a divider for outputting the ratio of the optical signal output from either one of the light receiving means for the first component and the optical signal output from the light receiving means for the second component to the strength-monitored signal output from the strength detection means.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring of high precision by use of a quotient signal can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the subtractor further comprises: a first gain adjuster for adjusting the strength of the optical signal output from the light receiving means for the first component, and a second gain adjuster for adjusting the strength of the optical signal output from the light receiving means for the second component.
By this configuration, a wavelength monitoring device capable of arbitrarily adjusting a reference wavelength can be obtained.
The wavelength monitoring device according to the present invention is constructed such that when the wavelength of a laser light input to the first birefringent crystal is xcex, the difference between the refractive index in the fast axis direction of the first birefringent crystal and that in the slow axis direction of the same is xcex94n, and the length of the propagating direction of the laser light of the first birefringent crystal is L, then the value obtained by xcex2/(xcex94nL) becomes 0.8 nm or more.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring of a plurality of channels can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the lengths of the propagating direction of the first and second birefringent crystals are set in such a manner that the value of (dxcex94nA/dT+xcex1Axc2x7xcex94nA)xc2x7LA+(dxcex94nB/dT+xcex1Bxc2x7xcex94nB)xc2x7LB becomes zero.
By this configuration, a wavelength monitoring device that requires no correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that when the value of dxcex94nA/dT and that of xcex94nB/dT are both positive or both negative, the first and second birefringent crystals are disposed such that the fast axis direction of the first birefringent crystal coincides with the slow axis direction of the second birefringent crystal, whereas the slaw axis direction of the first birefringent crystal coincides with the fast axis direction of the second birefringent crystal.
By this configuration, a wavelength monitoring device that requires no correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that when either one of the value of dxcex94nA/dT and that of xcex94nB/dT is positive, and the other one is negative, the first and second birefringent crystals are disposed such that the fast axis direction of the first birefringent crystal and that of the second birefringent crystal coincide with each other, whereas the slow axis direction of the first birefringent crystal and that of the second birefringent crystal also coincide with each.
By this configuration, a wavelength monitoring device that requires no correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the lengths of the propagating direction of the first and second birefringent crystals are set in such a manner that the value of (dxcex94nA/dT+xcex1Axc2x7xcex94nA)xc2x7LA+(dxcex94nB/dT+xcex1Bxc2x7xcex94nB)xc2x7LB becomes zero, and also the value of xcex2/(xcex94nxc2x7LAxe2x88x92xcex94nxc2x7LB) satisfies a desired value.
By this configuration, a wavelength monitoring device that does not require any correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the lengths of the propagating direction of the first and second birefringent crystals are set in such a manner that the value of (dxcex94nA/dT+xcex1Axc2x7xcex94nA)xc2x7LA+(dxcex94nB/dT+xcex1Bxc2x7xcex94nB)xc2x7LB becomes zero, and also the value of xcex2/(xcex94nxc2x7LA+xcex94nxc2x7LB) satisfies a desired value.
By this configuration, a wavelength monitoring device that requires no correction due to a temperature change can be obtained.
The wavelength monitoring device according to the present invention is constructed such that when the wavelength of the laser light input to said first birefringent crystal is xcex, the difference between the refractive index in the fast axis direction of said first birefringent crystal and that in the slow axis direction of the same is xcex94nA, the length of the propagating direction of the laser light of said first birefringent crystal is LA, the difference between the refractive index in the fast axis direction of said second birefringent crystal and that in the slow axis direction of the same is xcex94nB, and the length of the propagating direction of the laser light of said second birefringent crystal is LB, then the value of xcex2/(xcex94nxc2x7LAxe2x88x92xcex94nxc2x7LB) is set to be 0.8 nm or more.
By this configuration, a wavelength monitoring device capable of performing wavelength monitoring of a plurality of channels can be obtained.
The wavelength monitoring device according to the present invention is constructed such that when the wavelength of the laser light input to said first birefringent crystal is xcex, the difference between the refractive index in the fast axis direction of said first birefringent crystal and that in the slow axis direction of the same is xcex94nA, the length of the propagating direction of the laser light of said first birefringent crystal is LA, the difference between the refractive index in the fast axis direction of said second birefringent crystal and that in the slow axis direction of the same is xcex94nB, and the length of the propagating direction of the laser light of said second birefringent crystal is LB, then the value of xcex2/(xcex94nxc2x7LA+xcex94nxc2x7LB) is set to be 0.8 nm or more.
By this configuration, a wavelength monitoring device capable of performing a wavelength monitoring of a plurality of channels can be obtained.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a YVO4 crystal, and the second birefringent crystal is made of a LiNbO3 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a YVO4 crystal, and the second birefringent crystal is made of a CaCO3 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a YVO4 crystal, and the second birefringent crystal is made of a TiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a YVO4 crystal, and the second birefringent crystal is made of a SiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a LiNbO3 crystal, and the second birefringent crystal is made of a CaCO3 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a LiNbO3 crystal, and the second birefringent crystal is made of a TiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a LiNbO3 crystal, and the second birefringent crystal is made of a SiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a CaCO3 crystal, and the second birefringent crystal is made of a TiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a CaCO3 crystal, and the second birefringent crystal is made of a SiO2 crystal.
The wavelength monitoring device according to the present invention is constructed such that the first birefringent crystal is made of a TiO2 crystal, and the second birefringent crystal is made of a SiO2 crystal.
The method of adjusting a wavelength monitoring device according to the present invention includes the step of inclining the first birefringent crystal by rotating it about an axis perpendicular to the propagating direction of the laser light input to the first birefringent crystal.
By this method, such a good effect as an easy adjustment of the wavelength monitoring device can be obtained.
The method of adjusting a wavelength monitoring device according to the present invention includes the step of inclining either one or both of the first and second birefringent crystals by rotating them about an axis perpendicular to the propagating direction of the laser light input to the first and second birefringent crystals.
By this method, such a good effect as an easy adjustment of the wavelength monitoring device can be obtained.
The wavelength stabilizing light source according to the present invention is constructed such that it comprises: a semiconductor laser, a wavelength monitoring device for inputting a laser light incident from the semiconductor laser, and a laser drive control device for activating the semiconductor laser, and controlling the oscillated wavelength of the semiconductor laser by use of a wavelength-monitored signal output from the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source capable of stabilizing the wavelength of a laser light in high accuracy can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that the laser drive control device controls the oscillated wavelength by adjusting the current injected to the semiconductor laser, by use of the wavelength-monitored signal output from the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source whose oscillated wavelength is readily controlled can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that the laser drive control device controls the oscillated wavelength by adjusting the temperature of the semiconductor laser, by use of the wavelength-monitored signal output from the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source whose oscillated wavelength is readily controlled can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that the laser drive control device controls the oscillated wavelength by adjusting the length of a resonator of the semiconductor laser, by use of the wavelength-monitored signal output from the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source whose oscillated wavelength is readily controlled can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that the laser drive control device controls the oscillated wavelength by adjusting the periodic cycle of a diffraction grating provided to the semiconductor laser, by use of the wavelength-monitored signal output from the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source whose oscillated wavelength is readily controlled can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that a laser light collimating means for collimating the laser light emitted from the semiconductor laser is provided between the semiconductor laser and the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source in which a collimated laser light is easily input to a wavelength monitoring device can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that a transmitter means for transmitting the laser light emitted from the semiconductor laser to the wavelength monitoring device is provided between the semiconductor laser and the wavelength monitoring device.
By this configuration, a wavelength stabilizing light source in which the semiconductor laser and the wavelength monitoring device can be used separately can be obtained.
The laser light stabilizing light source according to the present invention is constructed such that the semiconductor laser, the wavelength monitoring device and the laser drive control device are accommodated in one module.
By this configuration, a wavelength stabilizing light source that can be easily handled can be obtained.
The transmission system according to the present invention is constructed such that it is provided with a plurality of laser light stabilizing sources, and one or more than one transmission means for transmitting a laser light.
By this configuration, a transmission system having a plurality of baseband frequencies can be obtained.